This invention relates to a sprout inhibiting and/or anti-fungal composition for potatoes.
Sprouting, also referred to as shooting, Is a problem in the storage of potatoes. It leads to a potato quality loss as a result of lose of weight. Further, the turgor of the potatoes lessens (the potatoes become softer), and toxic products may be formed in the sprouts.
Sprouting can be inhibited by storing the potatoes at a temperature of 2.degree. C., but at such a low temperature reducing sugars are formed which give the potatoes, when (deep)fried, a brown color and cause them to taste sweet (Maillard reaction). For this reason the potatoes are typically stored at a temperature between 5 and 8.degree. C. At such a temperature the problem of the formation of reducing sugars is absent or considerably smaller, but upon prolonged storage sprouting is not entirely prevented.
Therefore, sprout inhibiting agents are necessary to maintain potato quality during storage, both in potatoes intended for direct consumption and in potatoes to be processed into potato products. Such sprouting inhibitors are used to inhibit sprouting over prolonged storage periods at lower temperatures, i.e., below 10.degree. C.
For over two decades now, chemical sprouting inhibitors have been successfully utilized to prevent sprouting or shooting during the storage of potatoes. Propham (IPC) and chlorpropham (CIPC), which were originally developed as herbicides, are utilized as sprout inhibitors on a large scale in Europe, while in America also maleic acid anhydride is used. In England, tecnazene is still being used as a sprout inhibitor.
These last two agents are probably going to be forbidden in the near future. The use of IPC will no longer be permitted in the EU as of April 1997. Also, the market for ecologically grown potatoes, that is, untreated potatoes or potatoes treated with as little chemical agent as possible, is rapidly expanding.
In international patent application WO-A-95/09536 it is proposed inter alia to control potato sprouting with a mixture of menthol and carvone. Carvone is a compound which is present in the essential oil of the seeds of the caraway plant (Carum carvi). This compound is of interest because it is registered as a food additive and has the so-called "GRAS" status (Generally Recognized As Safe). Moreover, it is possible to grow caraway on a commercial scale. This is already happening on a large scale in various countries both inside and outside Europe.
Sprouting, however, is not the only problem in the storage of potatoes. Attack of the potatoes by fungi is also an important obstacle. Fungi primarily lead to loss of potato quality inter alia in that the taste is affected. In a later stage, diseases, such as silver scurf, and even decay of the potatoes may occur. An the potatoes constitute an excellent nutrient medium for the fungi, theme reproduce rapidly, Thus a complete stock of potatoes may be lost through a minor attack of only a few potatoes. As the process involved here is irreversible, it is of great importance that fungi be repelled from the very outset.
For repelling fungi in potatoes, at present a wide range of synthetic control agents are used. These, however, must be applied in considerable amounts in order to accomplish an adequate effect. The necessity of such large amounts of synthetic fungicides not only entails substantial costs, but is also undesirable in view of the associated environmental effects.
What has accordingly been searched for is a method of repelling fungi in potatoes in a manner as effective as possible, while the amount of required synthetic agents is considerably reduced. What has also been searched for is an agent that is effective both in repelling fungi and in inhibiting potato sprouting.
Surprisingly, it has now been found that a combination of carvone and one or more fungicides leads to a synergistic effect both for repelling fungi and for inhibiting sprouting. It has been found that when potatoes are treated with a combination of carvone and one or more fungicides, fungi are more effectively repelled.
The sprout inhibiting and/or anti-fungal agent consisting of a combination of carvone and one or more fungicides is suitable for use in ware and starch potatoes. The agent according to the invention can also be used in the storage of seed potatoes, so that sprouting is temporarily inhibited and the development of fungi is counteracted.
The carvone used can be D(S(+))-carvone, but also L(R(-))-carvone or a mixture of D- and L-carvone, and can be of vegetable origin or semivegetable through preparation by chemical conversion from, for instance, citrus waste. D-carvone and L-carvone, when used separately, exhibit an equal amount of action and both can therefore be effectively used, separately as well as in a mixture.
The nature of the fungicides that are used in the composition according to the Invention is not critical and in principle a variety of fungicides can be used. It is preferred, however, to use as fungicide one or more compounds from the classes that are active against Helminthosporium spp., inter alia Helminthosporium solani, Phoma spp., inter alia Phoma exigua var. exigua and/or Phoma exigua var. foveata, Fusarium spp., inter alia Fusarium sulphureum, Fusarium solani and/or Fusarium solani var. ooeruleum, and/or Phytophthora spp., inter alia Phytophthora erythroseptica, as these are the fungi that cause most problems in potatoes. Highly suitable examples of compounds from these classes are imidazoles, such as imazalil and prochloraz, and benzimidazole's, such as carbendazim and thiabendazole, which are known to have a very good action against the fungi and microorganisms mentioned and others occurring in potatoes.
The mutual weight ratio of fungicide to carvone in the composition according to the invention is preferably in the range of 1:1 to 1:10, more preferably in the range of 1;2 to 1;5. The most preferred composition according to the invention contains 50 to 250 grams of imazalil and 400 to 600 grams of carvone per liter.
The composition can be used dry an a powder or granulate which is imparted to the potatoes as the storage space is being filled with them (this is the so-called basic treatment).
Instead of being used as a powder or granulate, the composition according to the invention can also be misted over the potatoes while they are being stored in the storehouse, as a liquid, emulsion, suspension or suspoemulsion, directly or mixed with a small amount of water.
Further, the sprout inhibiting and/or anti-fungal composition can also be contacted with the potatoes at a later stage during the storage period by misting or spraying in the storage space, with the support of fans in that space.
In that case, depending on the desired mode of application, the present composition can also comprise a suitable carrier, suitable solvents, fillers or other agents conventionally present.
Suitable powdered or granular carriers and fillers are starch and starch derivatives, clay, talcum and other silicas, sand, diatomaceous earth, calcium carbonate and calcium sulfate (gypsum) and the various (co)polymers which can be used as carriers.
For making a granulate, an inert carrier can be impregnated with a solution of carvone and fungicide(s).
Further, granules can be sprayed with a mixture of one or more fungicides and carvone.
Suitable for the application of the sprout-inhibiting and/or anti-fungal agent in a liquid form are solvents of mineral origin, including aliphatic or aromatic solvents or mixtures thereof, which may or may not be chlorinated. Examples of these solvents are xylene, dichloromethane, ketones, aldehydes, alcohols such as glycerols (for instance polyethylene glycol), or derivatives or mixtures thereof. It is also possible to use solvents of animal or vegetable origin, such as linseed oil, soy bean oil or derivatives thereof. It is also possible to use mixtures of such solvents of animal, vegetable and mineral origin.
It is further possible to use a paste. Pastes can be formed by adding thickeners, such as, for instance, synthetic or natural polymeric thickeners, to solutions and emulsions of the composition in the above-mentioned solvents.
It is also possible to use the composition in emulsion form. For preparing an emulsion, carvone and fungicides can be mixed in the desired ratio, whereafter an emulsifier and optionally water or a different solvent is added. Another possibility is that water or a solvent is provided with an emulsifier and is then mixed with a mixture of carvone and fungicide (s).
Suitable emulsifying agents for preparing an emulsion are cationic, anionic and non-ionic surface-active substances of animal, vegetable and mineral origin. Examples are Ca-dodecyl benzene sulfonates, nonyl phenol polyglycol ethers, ethoxylated fatty acid alcohols or amines or derivatives or combinations thereof.
The emulsifier or the mixture of emulsifiers is preferably present in an amount of 2-20% by weight, preferably 10-15% by weight, in the total mixture. The eventual emulsion preferably contains between 20 and 50% by weight of sprout inhibiting and/or anti-fungal composition.
The invention further relates to a method for inhibiting sprouting in potatoes and/or repelling fungi, in which potatoes are treated with carvone and one or tore fungicides.
Obviously, in a preferred method the above-discussed sprout inhibiting and/or anti-fungal composition is used. It should be noted, however, that it is also possible, in accordance with the invention, to treat potatoes separately with carvone and one or more fungicides shortly after each other, which, surprisingly, yields the same synergistic effect.
According to a variant, potatoes are first treated with one or more fungicides or a composition of carvone and one or more fungicides and the potatoes are subsequently treated with carvone a few more times. When after a first treatment with fungicide, optionally in combination with carvone, the potatoes are treated with carvone two or more times after successive periods of six weeks, sprouting is found to be controlled particularly efficiently. In a particularly favorable embodiment the potatoes, after the first treatment, are treated with a mixture of carvone and menthol, as is described in International patent application WO-A-95/09536.
It in customary to store potatoes in bulk or in large bins in the storage space, which is mostly insulated. By means of fans, cooler outside air can be passed through the potatoes. Optionally, the (outside) air, before being passed through the potato mass, can additionally be cooled further by means of cooling systems.
Storage outside in a pit, heap or wall, or in a clamp silo is used for starch potatoes at present, but a variant of this can also be used to store ware potatoes, This last, however, is less common.
For the storage of the potatoes, use can also be made of cells or boxes with a volume corresponding to the ventilation capacity.
The bulk potatoes are preferably dried first, stored for a few days at about 15.degree. C. and then cooled in about two weeks to the desired storage temperature to ensure proper wound healing of damaged potatoes. This period of wound healing is necessary to limit microbial attack and weight losses during storage. The wound healing period of the lot takes about 14 days. After the wound healing period, the potatoes are stored at the desired storage temperature, the temperature being regulated through outside air cooling or mechanical cooling.
The desired storage temperature is 2-4.degree. C. for seed-potatoes, 4-6.degree. C. for ware potatoes, 5-8.degree. C. for French fries and dry industry, and 7-10.degree. C. for chips.
After a sprouting dormancy of a few months after harvest, the potato (depending on variety, history and storage method) begins to exhibit an inclination to sprout. In the course of time, this inclination to sprout grows increasingly stronger.
If cooling takes place in a mechanical manner (so that the desired storage temperature can be reached rapidly), the chances of early sprouting are limited already. To inhibit sprouting in optimum manner., subsequently the sprout-inhibiting and/or anti-fungal mixture according to the present invention is applied.
As the risk of infection with fungi in immediate from the start, it is preferred to treat the potatoes with fungicides or the composition of fungicides and carvone already at the time of storing the potatoes in a storehouse or pit.
The so-called basic treatment consists of imparting the sprout-inhibiting and/or anti-fungal agent (in the form of, for instance, powder or granules), for instance on a conveyor which convoys the potatoes to the storage space. It is also possible to spray or atomize the sprout-inhibiting and/or anti-fungal composition over the potatoes (above the conveyor).
It is further possible to pass the composition according to the invention to the storage space via the air ventilation system. For this mode of application, the composition can for instance be atomized or sprayed into the air. For this purpose it is possible to combine a mixture of carvone and one or more fungicides with a gaseous carrier so as to facilitate introduction into the air stream.
The two treatments can also be combined or be performed one after the other.
In all cases, the sprout-inhibiting and/or anti-fungal agents will evaporate to a greater or lesser extent and so all potatoes to be treated will come into contact with the agent.
The application of the sprout-inhibiting and/or anti-fungal composition according to the invention preferably takes place in a manner such that the concentration of carvone and fungicide together in the air of the storage space is between about 2 and 20 .mu.g/l air and more particularly between about 5 and 10 .mu.g/l air. At values lower than about 5 .mu.g/l air, sprouting inhibition will not be guaranteed to a sufficient extent. Higher values than about 20 .mu.g/l air do not lead to longer sprout inhibition and therefore lead only to unduly large amounts of the composition being used.